Answer: The exit temperature of the gas in deg C is
.
Explanation:
The given data is as follows.
= 1000 J/kg K, R = 500 J/kg K = 0.5 kJ/kg K (as 1 kJ = 1000 J)
= 100 kPa,
We know that for an ideal gas the mass flow rate will be calculated as follows.
or, m =
=
= 10 kg/s
Now, according to the steady flow energy equation:
= 5 K
= 5 K + 300 K
= 305 K
= (305 K - 273 K)
=
Therefore, we can conclude that the exit temperature of the gas in deg C is
.
<u></u>
has greater effect.
<u>Explanation</u>:
![\eta_{\max }=1-\frac{T_{c}}{T_{A}}](https://tex.z-dn.net/?f=%5Ceta_%7B%5Cmax%20%7D%3D1-%5Cfrac%7BT_%7Bc%7D%7D%7BT_%7BA%7D%7D)
= Temperature of cold reservoir
= Temperature of hot reservoir
when
is decreased by 't',
= ![1-\frac{\left(\tau_{c}-t\right)}{T_{H}}](https://tex.z-dn.net/?f=1-%5Cfrac%7B%5Cleft%28%5Ctau_%7Bc%7D-t%5Cright%29%7D%7BT_%7BH%7D%7D)
![-(i)](https://tex.z-dn.net/?f=-%28i%29)
when
is increased by 'T'
![\eta_{i n c}=\frac{n+\frac{t}{T_{H}}}{\left(1+\frac{k}{T_{H}}\right)}-(ii)](https://tex.z-dn.net/?f=%5Ceta_%7Bi%20n%20c%7D%3D%5Cfrac%7Bn%2B%5Cfrac%7Bt%7D%7BT_%7BH%7D%7D%7D%7B%5Cleft%281%2B%5Cfrac%7Bk%7D%7BT_%7BH%7D%7D%5Cright%29%7D-%28ii%29)
![\eta_{\text {incre }} \ T_{c}>\eta_{\text {incre }} T_{\text {H }}](https://tex.z-dn.net/?f=%5Ceta_%7B%5Ctext%20%7Bincre%20%7D%7D%20%5C%20T_%7Bc%7D%3E%5Ceta_%7B%5Ctext%20%7Bincre%20%7D%7D%20T_%7B%5Ctext%20%7BH%20%7D%7D)
I’m crying looking at that.
Answer:
![L=107.6m](https://tex.z-dn.net/?f=L%3D107.6m)
Explanation:
Cold water in: ![m_{c}=1.2kg/s, C_{c}=4.18kJ/kg\°C, T_{c,in}=20\°C, T_{c,out}=80\°C](https://tex.z-dn.net/?f=m_%7Bc%7D%3D1.2kg%2Fs%2C%20C_%7Bc%7D%3D4.18kJ%2Fkg%5C%C2%B0C%2C%20T_%7Bc%2Cin%7D%3D20%5C%C2%B0C%2C%20T_%7Bc%2Cout%7D%3D80%5C%C2%B0C)
Hot water in: ![m_{h}=2kg/s, C_{h}=4.18kJ/kg\°C, T_{h,in}=160\°C, T_{h,out}=?\°C](https://tex.z-dn.net/?f=m_%7Bh%7D%3D2kg%2Fs%2C%20C_%7Bh%7D%3D4.18kJ%2Fkg%5C%C2%B0C%2C%20T_%7Bh%2Cin%7D%3D160%5C%C2%B0C%2C%20T_%7Bh%2Cout%7D%3D%3F%5C%C2%B0C)
![D=1.5cm=0.015m, U=649W/m^{2}K, LMTD=?\°C, A_{s}=?m^{2},L=?m](https://tex.z-dn.net/?f=D%3D1.5cm%3D0.015m%2C%20U%3D649W%2Fm%5E%7B2%7DK%2C%20LMTD%3D%3F%5C%C2%B0C%2C%20A_%7Bs%7D%3D%3Fm%5E%7B2%7D%2CL%3D%3Fm)
Step 1: Determine the rate of heat transfer in the heat exchanger
![Q=m_{c}C_{c}(T_{c,out}-T_{c,in})](https://tex.z-dn.net/?f=Q%3Dm_%7Bc%7DC_%7Bc%7D%28T_%7Bc%2Cout%7D-T_%7Bc%2Cin%7D%29)
![Q=1.2*4.18*(80-20)](https://tex.z-dn.net/?f=Q%3D1.2%2A4.18%2A%2880-20%29)
![Q=1.2*4.18*(80-20)](https://tex.z-dn.net/?f=Q%3D1.2%2A4.18%2A%2880-20%29)
![Q=300.96kW](https://tex.z-dn.net/?f=Q%3D300.96kW)
Step 2: Determine outlet temperature of hot water
![Q=m_{h}C_{h}(T_{h,in}-T_{h,out})](https://tex.z-dn.net/?f=Q%3Dm_%7Bh%7DC_%7Bh%7D%28T_%7Bh%2Cin%7D-T_%7Bh%2Cout%7D%29)
![300.96=2*4.18*(160-T_{h,out})](https://tex.z-dn.net/?f=300.96%3D2%2A4.18%2A%28160-T_%7Bh%2Cout%7D%29)
![T_{h,out}=124\°C](https://tex.z-dn.net/?f=T_%7Bh%2Cout%7D%3D124%5C%C2%B0C)
Step 3: Determine the Logarithmic Mean Temperature Difference (LMTD)
![dT_{1}=T_{h,in}-T_{c,out}](https://tex.z-dn.net/?f=dT_%7B1%7D%3DT_%7Bh%2Cin%7D-T_%7Bc%2Cout%7D)
![dT_{1}=160-80](https://tex.z-dn.net/?f=dT_%7B1%7D%3D160-80)
![dT_{1}=80\°C](https://tex.z-dn.net/?f=dT_%7B1%7D%3D80%5C%C2%B0C)
![dT_{2}=T_{h,out}-T_{c,in}](https://tex.z-dn.net/?f=dT_%7B2%7D%3DT_%7Bh%2Cout%7D-T_%7Bc%2Cin%7D)
![dT_{2}=124-20](https://tex.z-dn.net/?f=dT_%7B2%7D%3D124-20)
![dT_{2}=104\°C](https://tex.z-dn.net/?f=dT_%7B2%7D%3D104%5C%C2%B0C)
![LMTD = \frac{dT_{2}-dT_{1}}{ln(\frac{dT_{2}}{dT_{1}})}](https://tex.z-dn.net/?f=LMTD%20%3D%20%5Cfrac%7BdT_%7B2%7D-dT_%7B1%7D%7D%7Bln%28%5Cfrac%7BdT_%7B2%7D%7D%7BdT_%7B1%7D%7D%29%7D)
![LMTD = \frac{104-80}{ln(\frac{104}{80})}](https://tex.z-dn.net/?f=LMTD%20%3D%20%5Cfrac%7B104-80%7D%7Bln%28%5Cfrac%7B104%7D%7B80%7D%29%7D)
![LMTD = \frac{24}{ln(1.3)}](https://tex.z-dn.net/?f=LMTD%20%3D%20%5Cfrac%7B24%7D%7Bln%281.3%29%7D)
![LMTD = 91.48\°C](https://tex.z-dn.net/?f=LMTD%20%3D%2091.48%5C%C2%B0C)
Step 4: Determine required surface area of heat exchanger
![Q=UA_{s}LMTD](https://tex.z-dn.net/?f=Q%3DUA_%7Bs%7DLMTD)
![300.96*10^{3}=649*A_{s}*91.48](https://tex.z-dn.net/?f=300.96%2A10%5E%7B3%7D%3D649%2AA_%7Bs%7D%2A91.48)
![A_{s}=5.07m^{2}](https://tex.z-dn.net/?f=A_%7Bs%7D%3D5.07m%5E%7B2%7D)
Step 5: Determine length of heat exchanger
![A_{s}=piDL](https://tex.z-dn.net/?f=A_%7Bs%7D%3DpiDL)
![5.07=pi*0.015*L](https://tex.z-dn.net/?f=5.07%3Dpi%2A0.015%2AL)
![L=107.57m](https://tex.z-dn.net/?f=L%3D107.57m)